OLEDs have been actively studied and developed because of their capabilities of emitting light of high brightness at a low driving voltage. An OLED generally comprises a pair of opposing electrodes having therebetween a light emitting layer or a plurality of organic layers including a light emitting layer. With an electric field applied to the opposing electrodes, electrons and holes are injected from the cathode and the anode, respectively, into the light emitting layer, where they are recombined to form excitons, which emit light. Otherwise, energy is transferred from the excitons to create excitons of other molecules, which emit light.
JP-A-2002-305083 discloses an organic phosphorescent electroluminescent device of which the light emitting layer contains an organic metal complex containing at least one metal selected from the groups 7 to 11 of the Periodic Table and an organic metal complex represented by the formula (I) shown in JP-A-2002-305083. The publication specifically recites a laminate structure having an electron transporting layer comprising tris (8-hydroxquinoline) aluminum complex (Alq) as an electron transporting material and a hole blocking layer comprising an aluminum complex (designated HB-12) provided between the light emitting layer and the electron transporting layer. Therefore, the device disclosed is still insufficient in luminescence efficiency and durability. Development of an OLED with higher luminance, higher luminescence efficiency, and improved durability has been keenly awaited.